The present invention relates to a new and improved construction of a fluid-actuated drive arrangement, especially a traction and thrust drive.
Generally speaking, the fluid-operated or fluid-actuated drive of the present development is of the type containing a piston-and-cylinder unit which possesses a piston rod connected with a piston guided for to-and-fro movements within the cylinder. The piston rod transmits the traction and/or thrust or compressive forces.
With state-of-the-art pneumatic or hydraulic drives utilizing a rigid piston rod and the thrusting-out of the piston rod in the extension of the cylinder requires a free space, the length of which corresponds to the length of the stroke of the piston-and-cylinder unit. Significant in this regard are, for instance, German Patent Publication No. 2,842,116 and the cognate U.S. Pat. No. 4,229,134, granted Oct. 21, 1980. The spatial requirements of such type of drives therefore amounts to more than twice the displacement stroke which, in turn, especially in the case of drives working with large strokes results in an appreciable installation length.
There are already known to the art different drives or drive arrangements which work without any rigid piston rod for the purpose of avoiding the previously explained drawbacks.
According to one proposed solution of this type there is totally dispensed with the use of a piston rod. The power transmission between the to-and-fro driven piston and the object to be moved is accomplished by means of a coupling element which is directly connected with the piston and extends outwardly through a slot provided at the cylinder jacket or shell. However, complicated measures must be carried out in order to seal the cylinder along the region of the slot and to preclude the entry of foreign particles or contaminants such as, for intance, dust into the interior of the cylinder. Moreover, this solution is afflicted with the drawback that the movement of the coupling element is limited to the region of the cylinder, and additionally, only can be accomplished along the lengthwise axis of the cylinder. Hence, the movement of the piston cannot be transmitted to a random site located remote from the cylinder without resorting to the use of additional measures.
According to another prior art drive construction, there is used, instead of the piston rod, a cable which can be coupled with the object to be moved. The cable is affixed at opposite sides or faces of the piston at such piston faces and is guided outwardly through the cylinder heads. The power or force transmission from the piston to the object to be moved is accomplished by the portion of the cable which always is under tensile load. While it is indeed possible to appreciably reduce the installation length to the length of the piston-and-cylinder unit and nonetheless to transmit the motion of the piston directly to a random site or location, still there is required a certain constructional and spatial expenditure for guiding the cable from one piston face to the coupling location where the cable is coupled with the object to be moved and from such coupling location back again to the other piston face. Additionally, deflection rolls for the cables as well as seals for sealing the throughpass locations of the cable must be provided at both cylinder heads.